src: use namespace prefix osmo_timer* for timer functions

Summary of changes:

s/struct timer_list/struct osmo_timer_list/g
s/bsc_add_timer/osmo_timer_add/g
s/bsc_schedule_timer/osmo_timer_schedule/g
s/bsc_del_timer/osmo_timer_del/g
s/bsc_timer_pending/osmo_timer_pending/g
s/bsc_nearest_timer/osmo_timers_nearest/g
s/bsc_prepare_timers/osmo_timers_prepare/g
s/bsc_update_timers/osmo_timers_update/g
s/bsc_timer_check/osmo_timers_check/g
diff --git a/openbsc/src/osmo-bsc_nat/bsc_ussd.c b/openbsc/src/osmo-bsc_nat/bsc_ussd.c
index 0392e9b..5d599c7 100644
--- a/openbsc/src/osmo-bsc_nat/bsc_ussd.c
+++ b/openbsc/src/osmo-bsc_nat/bsc_ussd.c
@@ -59,7 +59,7 @@
 
 	close(con->queue.bfd.fd);
 	bsc_unregister_fd(&con->queue.bfd);
-	bsc_del_timer(&con->auth_timeout);
+	osmo_timer_del(&con->auth_timeout);
 	write_queue_clear(&con->queue);
 	talloc_free(con);
 }
@@ -168,7 +168,7 @@
 		bsc_nat_ussd_destroy(conn->nat->ussd_con);
 
 	LOGP(DNAT, LOGL_ERROR, "USSD token specified. USSD provider is connected.\n");
-	bsc_del_timer(&conn->auth_timeout);
+	osmo_timer_del(&conn->auth_timeout);
 	conn->authorized = 1;
 	conn->nat->ussd_con = conn;
 }
@@ -179,7 +179,7 @@
 
 	conn->auth_timeout.data = conn;
 	conn->auth_timeout.cb = ussd_auth_cb;
-	bsc_schedule_timer(&conn->auth_timeout, conn->nat->auth_timeout, 0);
+	osmo_timer_schedule(&conn->auth_timeout, conn->nat->auth_timeout, 0);
 
 	msg = msgb_alloc_headroom(4096, 128, "auth message");
 	if (!msg) {